GAMEBOY COLOR - BAD BUTTON TROUBLESHOOTING First you need to open the unit up and for this you will need a small phillips screwdriver and the proprietary gameboy tri-winged, when open the first thing to do is to clean the pcb contact point and also the rubber with alcohol (isopropyl/ethanol), you can detach the screen from the front and lay it firm on the pcb and you can start the gameboy with the back mounted and also with inserted gamepak and batteries, this way you can try the buttons while on, if the now cleaned pcb contact points still have a dark surface that won't go away with rubbing alcohol on it you can scratch the surface a little bit to remove some of the oxide build up and rub it with more alcohol after, now take one of the rubber buttons and try it on every contact point to see that every button respond and that the respond fast enough. If this worked good for you, if it didn't then this guide is actually made for you, it's very uncommon but it happens and somewhere on the pcb there's is a break in the one of the pcb's pathways, now this is where the hard part comes in. First the control buttons should measure 3V between them (3.18V depends on condition of batteries). Every button also has a testpoint P00-P07 which should lead to the + of each button, the – of all buttons should be connected and it should also be to the ground, each buttons + should lead to a via hole, measure it and see that they are connected, the via holes comes out on the other side and they are under the game pak connector, but they will lead to a new via hole.